


a piece of him

by Germindis



Category: Undertale (Video Game)
Genre: Abuse, Alternate Universe - Undertail (Undertale), Blood and Gore, Blood and Torture, Blood and Violence, Broken Bones, Ecto-Genitalia (Undertale), Ecto-Vagina (Undertale), Emotional/Psychological Abuse, Genital Torture, Gore, Guro, M/M, Medical Torture, Non-Consensual Violence, Physical Abuse, Rape, Rape/Non-con Elements, Sanster, Sexual Abuse, Sexual Violence, Tentacle Dick, Tentacle Rape, Torture, Verbal Abuse, Violence, noncon
Language: English
Status: Completed
Published: 2020-08-19
Updated: 2020-08-19
Packaged: 2021-03-05 23:21:40
Rating: Explicit
Warnings: Graphic Depictions Of Violence, Rape/Non-Con
Chapters: 1
Words: 4,620
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/25923523
Author URL: https://archiveofourown.org/users/Germindis/pseuds/Germindis
Summary: Gaster discovers that skeletons can have their limbs popped off with no consequences. So, what else can be done to a skeleton? His experiments snowball into a terrifying situation for Sans.Contains rape, medical torture, and detailed gore.
Relationships: W. D. Gaster & Sans, W. D. Gaster/Sans
Comments: 15
Kudos: 77





	a piece of him

**Author's Note:**

> This was written for a collaboration with [nsfwgarbagedump](https://twitter.com/nsfwgarbagedump), who drew a comic based on the text. They produced some truly lovely, visceral pages. Please check them out!
> 
> Here are the comic pages: [noncon Sanster medical torture / rape comic](https://twitter.com/nsfwgarbagedump/status/1296232202611707917)
> 
> Many corrections and excellent suggestions were made by the ever so clever [Ravvi](https://archiveofourown.org/users/Ravvi/pseuds/Ravvi). You have her to thank especially for any time a description was vague in the first draft, she said "mOrE!" and it became what this final draft is.
> 
> And now to get...cracking. :)

“Do you think you get ‘heads’ in life, Sans?”

Sans snorted with laughter. The old man never failed to make him laugh, but specifically because he chronically mistold jokes. Sans’s body, from the neck’s vertebrae down, sat across the room from them in a beaten wicker chair while Sans’s skull was looking up at Gaster, balanced on a peg on the counter like a...well, like a head on a pike.

“I think you mean ‘ahead in life,’ Doc.”

Gaster turned from the tray of tools by his side, his lopsided features stretching in mellow surprise.

“That’s not what I said? Well then.”

Sans snickered.

Probably, the joke was meant to put Sans at ease with the situation. Sure, it should be unnerving, but Sans was actually a little embarrassed to admit, even to himself, that it was strangely pleasant. It didn’t seem like it should be pleasant, having his skull separate from his body. That sounded like a kind of perversion. But ever since Gaster had popped Sans’s neck, Sans’s head filled with a floating dreaminess that twinkled through the spaces behind his sockets like starlight.

It wasn’t the first time the doctor had separated Sans’s limbs for an experiment. Gaster finding out it could be done was an accident—Sans had pulled too hard on a stubborn door in the labs and, hilariously, his arm had popped right out. Gaster, having never met a skeleton monster before Sans, was captivated by the discovery; it was most likely because Sans hadn’t seemed too upset or shocked about the mishap. Skeleton bodies would do that from time to time. After that, though, the doctor became increasingly sidetracked from his other studies by pulling out Sans’s limbs, testing how the thin magical connection to the separated parts functioned, and then putting them back in. Now things had come to (Sans had to laugh again) a head.

Gaster selected a thick silver pen from his tool tray, a cord trailing from the implement through a c-shaped holder for the pen, and down to an outlet on a metal panel of the equipment tray. The anticipation for the shock to come made Sans feel a bit giddy.

The tip of the pen touched Sans’s tooth. Gaster had to do a funny little waddle that turned his whole body to look behind him—the hump on his back that made him hunch prevented him from swiveling his neck—and they both saw the effect of the low voltage. Across the room, in the chair, the toes on Sans’s body curled.

“Amazing!” The doctor’s enthusiasm was contagious, even if him patting the side of Sans’s face was awkward. If Sans didn’t feel as high as he did, he might think it was a little condescending. “5 whole meters and a skeleton can still feel it! We’ll need to try this in a less cramped room next time...” 

Next time. So his curiosity about Sans wasn’t sated yet. Gaster touched Sans’s face again, adjusting his skull slightly.

“One more for today. Can you nod your head?”

Sans gave it a try. His head had just been moved by Gaster, after all. But attempting it himself resulted in the disjointed sensation of being certain he was doing it, yet with no change in the relationship between his head and gravity.

“Hm, no...” Gaster jot down a note on a pad that was jumbled with the rest of his poorly organized tools on the tray. “And your body? Anything?”

Sans gave that a try next. None of the signals were reaching, clearly, which almost made him wonder if he remembered how to make himself move in the first place.

“Nah, Doc. Not an inch.”

Gaster muttered as he took another note.

“Inches, yes, well, an intelligent assistant should know that the imperial system is hardly scientific...”

Sans heard a silly giggle coming from his own mouth, and Gaster looked up at him from the notepad to smile. Maybe Gaster was getting the hang of jokes after all. 

Gaster carefully lifted Sans’s skull from the peg, carrying him back towards his body and having to shuffle around more misplaced equipment. He was not as concerned as he perhaps should have been, as head royal scientist, about jostling the brightly colored tubes that contained painstakingly collected, high-concentrate magic attributes. Gaster merely hummed in his absent-minded way like the rainbow set of vials had got in his way on purpose. 

When they reached Sans’s body, instead of reattaching his head right away, Gaster balanced it under one arm like a football and reached for Sans’s shoulder with another hand.

“One more thing...”

Gaster slid his hand from the shoulder down to Sans’s chest. Tingles sprouted from Sans’s spine like trapped bubbles underwater escaping to the surface. He made a reactive, breathy noise before he realized what happened. Gaster looked down at Sans’s head under his arm.

“You can still feel that?”

Sans gave an affirmative ‘mhm’ that sounded sleepy. Even without being touched, this whole time his body felt like it was immersed in a fizzy bath, dreamlike and soothing. With what intellect was still intact, Sans had a notion that this was his magic’s way of pretending his body was still attached to him, like a phantom limb. 

“Interesting...”

Sans’s head was reconnected with an insistent push and a loud pop. The buzz of magic accepting the displaced body part back in its home was euphoric.

Gaster was gazing at him, one of his floating hands summoned to hold his own chin in contemplation.

“You didn’t take any damage from being separated, either...” Two more of Gaster’s floating hands wafted down to land on his hips. “To think, we still know so little about the depths of how magic connects us. A skeleton monster’s body raises so many questions...”

Sans experienced a sudden prickle of nerves. As small as it was, it was almost alarming in how different it felt from his ‘headspace’ only seconds ago. Maybe it was withdrawal from the high that was making him overly sensitive, but there was something about Gaster referring to Sans as ‘a skeleton monster.’ Like he was a subject.

Sans found himself touching his own chest where Gaster had a moment before, just as suddenly feeling self conscious, and the tiniest needle of...what even was it...shame? that Gaster had touched him in a way that didn’t seem entirely necessary for an experiment. A little too intimate. But that was silly, wasn’t it?

Sans shrugged his shoulders like he was shrugging off the thoughts.

“If we do too many more of those, Doc, I might have a bone to pick with you, heh.”

Gaster stared harder at Sans, face neutral and hand still stroking his chin.

“Hm...yes...I’ll pick another bone too, next time...we can try more than one at once...”

Sans failed to laugh at that one.

  
  


The experiments were all but forgotten by the time Sans entered the labs after a full day away. Two jobs and Papyrus were a lot to juggle while he kept up his internship here, but he had high hopes that nabbing this special position would turn into something more. How could it not? The royal scientist didn’t pick just anyone to assist in his work.

Sans hung up his ratty winter coat at the entrance, sliding his arms into his as yet pristine lab coat, the nicest thing he owned. 

And then his extended arm was grabbed at the wrist by a floating hand.

“Hey! Whoa! I just got here, Doc!”

He wasn’t sure if the hand could ‘hear’ him without Gaster immediately present, but he talked to it as though it were Gaster anyways. Maybe if his separated bones could feel things across a room, Gaster knew what his hands knew wherever they were? If it was possible to be ignored by such a thing, Sans was ignored by the hand as it dragged him deeper into the lab.

He was brought to a door he didn’t think he’d ever gone through before. Another of Gaster’s hands turned the knob to show them in.

Inside, Gaster was waiting by a long metal table. The table was propped at an angle by a mechanism of gears, very solid-looking straps screwed in at four spots parallel to each other. Sans was pretty sure he’d seen this setup on the cover of an old science fiction novel.

“What’s...”

He lost his words at the sight. Any moment now, the doctor was going to badly tell a joke, do his silly little waddle over to Sans, and they would do something like crack a melon open on the table. He didn’t anticipate Gaster’s hands shoving him by the small of his back the rest of the way into the room and shutting the door behind him.

“Come here, Sans, we’re ready to start.”

The hand on Sans’s wrist tugged harder, making him grunt. 

“Watch it, Doc, I’m delicate.”

It was just the kind of thing he’d say to take the piss, but Gaster didn’t even smile. He looked thoughtful.

“Yes. Very delicate...”

A creeping chill went up Sans’s spine. He was so caught off guard that the next yank from the hand unbalanced him. He would have face planted on the concrete floor, but a flurry of Gaster’s hand constructs took him up and carried him to the table. 

They then began to strip off his clothes. Sans watched the lab coat he’d spent days upon weeks studying to feel like he’d earned, cast carelessly on the floor like a piece of garbage.

“What...what gives?”

He was too numb with shock to fight his shirt being unbuttoned, shoes and socks stripped, one piece of clothing after another joining the pile on the floor.

“They’ll only get in the way. We want to be able to clearly see all results.”

This didn’t feel right. Especially as Sans’s pants were pulled down, and his hands automatically clasped in front of his pelvis in modesty. Participating in tests was one thing, but didn’t the doctor have smocks, or something? Getting his clothes flung off seemed like it belonged more in a summer frat party setting, a very awkward but earnest first try at seduction.

What _was_ this?

Sans didn’t like to contemplate that his question was being answered by the hands spreading him flat on his back, locking him in with the straps.

The table dropped a foot with a soul-churning lurch of the mechanism, and Gaster loomed over him. He was wielding a heavy power tool with a cord...an electric saw.

“Wait. Gaster.” Sans didn’t like the panic creeping into his voice. An insanely stupid and prideful part of his brain restrained him from struggling because it would make him look pitiful. He could handle a simple experiment, couldn’t he? That must be all this was. “At least. Tell me what we’re doing.”

Gaster’s head tilted, making his unbalanced face appear even more crude, like a poor drawing.

“Ah. If you’re interested.” He flipped a switch with a thumb, and the saw hummed to hideous life. “It’s possible to take your bones apart, so the logical next step is to see if areas other than joints can be as easily severed without consequence.” The saw pointed delicately at an angle, towards Sans’s left humerus, Gaster etching it through the air just above to illustrate a potential cut. The proximity made Sans’s bones vibrate with danger. “Here...to here.”

Sans gulped in air.

“No. You can’t do that.”

The saw turned off, swinging back towards Gaster.

“No?”

He picked up a permanent marker, popping the cap off and drawing a thick blue line across the upper part of Sans’s humerus, where he’d indicated with the saw.

“It will be healed right away. There’s no reason to object.”

Sans kind of thought there was some other reason to object to this being done to him, but when it was put that way, Gaster had managed to make it sound shameful to refuse. Just an experiment.

This wasn’t just an experiment. This was insane.

“Doc...”

Sans’s voice cracked at the end of the syllable. The restraints were oppressively tight over his wrists and ankles, making him hyper aware of the staccato percussion of bone trembling on metal. 

“Did you know...” One of Gaster’s hands traced a finger in an intimate trail down the side of Sans’s skull to his jaw, turning it to face him. “...you’re beautiful when you’re frightened.”

No. No.

Sans arched his spine, the only part of his body that could fight his position even a small bit. This wasn’t the doctor. Some pod had grown in the night and body-snatched him, replacing him with whatever this was. Because the doctor wouldn’t be nonchalantly marking all the places he planned to slice Sans up, doing a stupid hobbling shuffle around the table to reach more of his body. He seemed satisfied once there were marks on each of Sans’s limbs, his hands, on his ribs, and his collarbone.

He couldn’t get away. Sans’s brain unhelpfully reminded him that the ability to teleport would have come in handy now, but Sans had fallen asleep over the chapter on practical teleportation in his Liminal Magic textbook. He hadn’t needed it for the final exam, and passing the course had been hard enough.

Blade embedded in bone. Sans saw blazing white, and something beyond that—a spectral agony too bright for vision. His bone rang like a siren, the saw made hot friction with the air, an unbearable smell of meat and overheated metal filling the room as the outer layer gave way to scalded marrow. It was still going, the heat of the saw breathing on him. How thick was one bone? Sans couldn’t hear himself scream, but he felt his body convulse, every atom fighting to stay alive. 

The slice was clean, too perfectly clean for the way Sans had been bucking on the table, for the unreality of Gaster mutilating him.

For a breathless moment as he strained on the table, Sans had a nightmare vision of Gaster healing over the broken stump, leaving Sans with less than half an arm. But Gaster touched his finger along the wound and joined the bone just as it was before, the only sign left of the trauma being a strip of off-white that would eventually cool into a scar. If he didn’t know better about how healing magic worked, Sans could swear he still felt the pain of the cut, echoes of it pulsing up and down his arm from the point of injury.

Gaster’s face as he eyed his work was oddly sweaty.

“The next one, then,” he breathed.

Instead of going methodically, Gaster went right to the clavicle next, the touch of an extra hand making Sans shiver in disgust as it pressed him down for balance. 

Sans tried holding back a whimper but that only made the sound longer and higher. It must have been less than ten seconds that the bone was sliced before being healed, but the heat stayed. The gaseous particles of burnt collagen hung around in his nasal aperture. 

Amidst the dizzying weakness that made his body shake, Sans felt a weighty lump press into his left hand, from the side where Gaster was standing. It rubbed against him, giving the fluid twitch of something organic. That couldn’t be.

But it rubbed on him more insistently, and it became undeniable that Gaster was humping Sans’s hand with his erection.

“Wh...”

Sans couldn’t even speak an objection to that violation. Gaster was making him scream and suffer on his torture table, and he was getting turned on by that.

Gaster jerked Sans’s arm, fidgeting and grunting as Sans’s fingers brushed the warmth in his pants. Apparently unsatisfied with that, Gaster picked the saw back up, stretching Sans’s arm out tight. Sans gasped.

“No—please—!”

The saw sank through radius, then ulna. This time shock was delaying the pain, but the broken cross section that stared at Sans looked like runny scrambled eggs, and now that was all he could think about. That, and his hand being manipulated to stroke Gaster between the legs, palming his repulsive hard on while it grew against him. The runny eggs were swimming, squirming out of his arm and pooling on the table, making Sans’s hollowing bones colder. Sans’s skull hit metal with a clang.

Sans awoke to Gaster hunched over him, on his hands and knees on the table where Sans was still strapped down, still naked. Sans could see three new off-white stripes on his right arm now, and some on both legs, so him passing out hadn’t slowed down Gaster’s enthusiasm. Gaster did wait, however, for Sans to consciously meet his eyes before slowly unzipping his pants.

Sans’s knees turned inward with a shudder. Not only did a sludgy, tar-like dick fall forward with a thump, but two extra tendrils on each side unfurled like sticky, ink-covered squid arms.

“Gaster...” Sans struggled to control himself. He was still barely processing the violence, and now Gaster was... “I, I just work here.” Sans gulped, and the sobs started coming out. “For college credit! I don’t, you can’t...”

“Yes, about that.” Gaster placed two fingers against the ischium of Sans’s pelvic bone, running them along it in a loop that ended at the pubic symphysis, where he began rubbing Sans mercilessly, agitating Sans’s magic into lighting the bone from within. “You’re rather bright, Sans, but not as bright as you are attractive. These clean white bones...”

Gaster held Sans’s groin to his, marring whatever cleanness the bones might have had as his prehensile cock smeared remnants of itself along Sans’s inner femur. 

“Surely you thought it was strange. You hardly had the best grades of all the applicants. I would have selected for stupider if I could, but there isn’t so much a call for a secretary position as there is for a lab assistant...” 

The haze of sick misery Sans had been subjected to finally boiled over into hot, humiliated anger.

“When someone gets as smart as you, do we all get the honor of getting an ugly, melted pancake for a face!”

Gaster’s fingers tweaked Sans’s pubic bone, forcing the pent up magic to fill out the inlet with the ghostly beginnings of a pussy. The black tendrils petting the soft outer lips got a small sound out of Sans, an intake of breath that trembled the air at too high a pitch. 

“I take. I take it back...”

He was arranged for the cock to enter him. It licked over the underside of the inlet like a tongue. Sans’s hips jolted in protest.

“Please don’t.”

It was all talk. Gaster had taken his head off, yes. He’d sliced his limbs apart. He was certainly the mad scientist type; that was established. But he wasn’t really going to sit here on top of him and rape him in this horrid little room.

The cock slithered in, parting the inner lips and rolling against the threshold of the opening. It spiraled inward like a corkscrew, widening Sans even as it delved deeper inside him. As it turned out, that was so the four tendrils could join the cock inside him. They each nudged at the stretched opening, the little noses of eager worms begging to violate Sans too.

“No...no...no, no...” Sans yanked at his arms, but the restraints had more integrity than his body. Each healed cut burned anew with the strain, making him buck in agony. The worms took advantage of the movement to dive into him, stretching him wide open all at once. “NO!”

Gaster’s hips touched his. All five of his awful appendages were shoved inside Sans. Pain lanced through Sans from his groin up to his arms, a sickly, feverish pain like his body wanted to puke itself out and start over. Like what was left after this was unrecoverable. 

A threatening creak made Gaster lift his hips just an inch, pulling out an inch of the slimy invasion. A floating hand stroked the pubic symphysis again, making Sans gasp and writhe on the edge of bursting into more tears. The fact that he didn’t cry made him feel like he was choking on that wretched stimulation, unable to purge it. The thin strip of cartilage that joined the bones of his pelvis looked distorted, bending upward unnaturally. Gaster hummed.

“Not wide enough...perhaps the magic can be persuaded to accommodate.” 

He withdrew, the whole mass of tentacles pulling out of Sans with too wet a pop. The tarry black was painted with blue and red streaks, scraped up magic and marrow from tearing Sans on the inside. The absence of pressure didn’t even feel like a relief, because now there was nothing to distract from the intense sting.

Gaster slid clumsily off the table, and Sans dimly fantasized about swatting him the rest of the way off so he’d crack his head on the concrete like a dropped egg.

The doctor returned with a vial pinched between two fingers. The hand holding the vial sailed smoothly over the table while, in contrast, the doctor had to grapple himself back up in an undignified manner. He settled before Sans again, hovering the little vial above Sans’s pelvis, right over the pubic symphysis. The contents were an acidic yellow, a hyper-saturated ethereal color that didn’t belong in the same space of existence as normal things. It was one of the lab’s precious containers of extracted magical attributes.

“Determination is a little crude, but some Justice should do the same in a high enough concentration. I only need a bit more room.”

Gaster tilted the tube, and the drizzle came down with the innocent hiss of bubbling soda. The ectoplasm blinked out in a blessed instant, but bone hit by the flow simply melted away, matter sloughing down in a gray ooze that blackened as it shriveled into next to nothing. Sans’s hips jerked forward and back of their own accord, a shriek escaping him that he didn’t recognize as his own voice. It was the voice of some tortured animal, if it were possible to hear a bug scream as it twisted upside-down under the glare of a magnifying glass. The vindictive burn tore through cartilage, ossein, and vessels. Sans’s soul relinquished with a splash.

A hand reached into Sans’s rib cage, removing his soul so Gaster could examine it while Sans twitched and whimpered under him. The soul was dripping, about half of the distressed magic within having decided to release in an effort to relieve the unbearable tension and fear. Gaster thumbed the mess with interest.

“It’s rare I see a monster completely lose control of himself like that. It was that painful?”

Sans’s skull was ringing. His eyes saw what his pelvis looked like now even if his brain stuttered in puzzling together the images and recognizing it as his own body. The pubic symphysis was completely obliterated, the ischium that used to be connected by it remained as jagged points like fork tines. A high keen rattled in his throat as he helplessly convulsed. 

So stupid. He’d already forgotten that Gaster had a reason to do that to him.

Gaster laid his hands on the mutilated stubs of ischium, and pulled outward. Like cracking open a crab. Sans screeched. 

“NoO—! Please—” He gasped out brokenly. “No, stop, no!”

The dripping tentacles were kissing the inlet, Gaster’s thumbs rubbing so tenderly, the force of Gaster’s intention waking the abused magic to light in the inlet again. Sans wheezed as it began to take shape, the translucent blue filling him out less naturally than before. It reached for bone to stick onto that didn’t exist anymore, starting an agonizing stretch upward, little bulbs of it praying to the ceiling like plants to the sun.

“It’s, god, Gaster, I can’t. Make it...stop please....”

This one time, out of all of the horrors of the day, Gaster actually looked up at Sans and seemed to consider him. A hand took up Sans’s chin, thumb brushing just under his teeth.

“I want you to beg.”

Sans’s soul stuttered. There was still just the ghost left in the back of his mind of the Gaster he’d thought he’d known, who’d endeared himself to him with his brilliance and bumbling and subtle manner that Sans had taken to be gentleness. Sans’s mouth opened, the pleas he desperately hoped could spare him even a small bit of this torture on the tip of his tongue.

Gaster’s hand gave Sans’s skull a light bounce.

“Beg me to use your mouth instead.”

A single breath came out of Sans, a trill of disbelief. He set his teeth, his eyes traveling from the fresh scars on his arms, to the puddle of him congealing fast under his pelvis and ribs, the bad joke that was left of his groin, to the doctor’s expectant face.

“You can’t...”

In response to that, Gaster tugged Sans’s pelvic inlet towards himself again, his writhing dick straining against the broken magic. Sans’s spine arched high, a demented squeal escaping him. The bite of his pelvis cleaving open struck through him with renewed fire. 

Sans wanted to scream and scream until he stopped having a voice, but instead a hoarse whisper came through his teeth.

“Please...use…” His teeth grit together. “Use my...mouth instead...”

Gaster released him.

“Say it again.”

The hand was petting Sans’s face, and that was how he felt the streaming tears as they were smeared around.

“Please use my mouth instead...”

“If you insist.”

Gaster’s lumbering body climbed up him, sitting his crotch over Sans’s face with his knees bent to either side of his skull, Sans’s pinned arms hugging them.

Sans’s reward was Gaster’s cock shoving down his throat, all foreplay done with as the monster’s hips got to gleefully fucking Sans’s skull. Sans’s insides were outsides and the melted parts of him were aggravating a rash in the joints of his hip bones, squeaking up and down the table with each thrust, and the pumping into his throat went on forever.

After forever, a waxy scum poured into his mouth, shooting out of the pulsing cock as Gaster’s hips trembled over him. Gaster’s finish oozed out of his nose and sockets, Sans’s magic too exhausted to absorb all of it. Gaster lifted himself off Sans’s face, strings of the goo sticking between them.

Gaster sighed. 

“A good lab assistant can certainly make himself useful.”

Sans broke down into heaving sobs. The goo in his skull swelled out of him in tears and spit, weeping in viscous drops that clung too long to his face.

“Please Doc. Please. I wanna go. Home...”

The doctor tipped off the table one leg at a time.

“Ah, home.” He adjusted his pants, tucking up cock and tentacles. “The apartment on the corner of First, above the grocery.” Sans’s soul quivered. It was still laying where Gaster left it, hovering by Sans’s lower spine, but the sensation of icy dread made its way through Sans’s whole body. Gaster looked down at Sans. “The apartment where your younger brother resides. Also a skeleton...one of the only two skeleton monsters of which I have ever known.” 

Words disappeared. Thoughts disappeared. Only the fear was left. Gaster groped over Sans’s pelvis, spreading the tingle of healing magic that would preserve his life but would never save the lost pieces.

“And skeletons are so very interesting to me...”

Sans’s hip bone was given a light pat, as if to announce the healing complete. 

“You will continue to assist me, won’t you?” 

**Author's Note:**

> You can find me on [Twitter](https://twitter.com/LeechMc) for naughty art, updates, and more horrible things happening to Sans.


End file.
